The use of algae in a variety of industrial processes for commercially important products is known and/or has been suggested. For example, algae have been used to make pigmentation agents, such as carotenoids; nutritional supplements, such as omega-3 fatty acids; and pharmaceuticals. Use of algae in mariculture as a food source for fish and crustaceans is also well known. Algae have also been suggested for use in the production of starting materials for the production of a diesel fuel substitute. Further, algae have been suggested for use in pollution control, such as for the uptake of carbon dioxide and in bioremediation applications.
Some wild-type algae are suitable for use in these various applications. However, it is recognized that by modification of algae to improve particular characteristics useful for the above-referenced applications, the relevant processes are more likely to be commercially viable. To this end, algal strains have been developed which have improved characteristics over wild-type strains. Such developments have been made by traditional techniques of screening and mutation and selection. Further, recombinant techniques have been widely suggested for algae. However, for a variety of reasons, recombinant transformation techniques have not been successfully developed for wide scale development of algae.
Over the past decade, genetic transformation has become routine for many organisms, including bacteria, yeast, mammalian cells and some higher plants. However, there has been little success mn developing transformation systems for eucaryotic microalgae, due partly to the recalcitrance of commonly-used algal species to standard transformation techniques and genetic markers. This phenomenon is likely to be due to the difficulty of introducing foreign DNA into the algal cell through the cell wall and to poor expression of commonly used transformation markers, such as neomycin phosphotransferase or other antibiotic resistance genes, by the algae. To date, the only eucaryotic microalgae for which there are reproducible transformation systems are the single-celled green alga Chlamydomonas reinhardtii and a closely related colonial species Volvox carterii. However, successful transformation of these organisms to date has required the use of homologous genes as selectable transformation markers. These protocols often require the development of auxotrophic mutants which can be transformed with plasmids containing wild-type homologous genes, rendering the cells prototrophic.
In view of the above discussion, a need exists for a genetic transformation system which is widely useful in algae.